Integrated Circuit (IC's) can include thousands or millions of transistors on a single chip. Operation of these transistors can generate significant heat in a small area. Hotspots can develop that can damage the IC device.
The temperature of the IC device can be monitored by an on-chip temperature-sensor circuit. When the monitored temperature exceeds a limit, the IC device can be protected, such as by reducing operating frequency or by shutting down parts of the IC device. Once the IC device has cooled, the frequency can be increased again, or more parts of the IC device may be powered back up.
Temperature-sensor circuits have a temperature sensitivity that is the slope of a plot of the circuit's voltage vs. temperature (V/T). This temperature sensitivity can shift due to gain errors. Gain errors may be caused by device mis-match, layout mis-match, DC offsets, or other circuit characteristics.
During calibration, the temperature-sensor circuit's output voltage can be measured at two or more temperature points to establish a straight line in the voltage vs. temperature plot. The slope of the line, in volts per degree C., can be obtained and used during normal operation to determine the temperature shifts corresponding to sensor voltage changes.
Such two-temperature-point calibration is undesirable, since the circuit must be measured at two different temperatures during calibration. The IC device may have to be placed in a temperature-controlled chamber or otherwise heated or cooled to obtain the second temperature measurement. Such heating may require 10 or more minutes. Expensive test equipment may be occupied during this heating period, or the product testing line may need to be expanded, increasing test and manufacturing costs.
More recently, single-temperature-point calibration has been used to eliminate the heating delay time. One temperature point is assumed to be absolute zero (−273.15° C.) where the temperature sensor circuit produces some pre-computed offset. Since the voltage vs. temperature line is anchored at absolute zero, only one other temperature point is needed to establish the line's slope or sensitivity. Thus calibration requires measuring the output voltage of the temperature sensor circuit at only 1 temperature point. This measured temperature point can be at room temperature, eliminating the need for a temperature chamber during calibration.
However, single-point temperature sensor calibration often suffers from a relatively small temperature sensing output range. Sometimes the temperature sensitivity can be tuned only over a short range. DC offsets in the circuit can cause inaccurate sensitivity readings. Calibration errors can occur when the 2nd, measured temperature point is incorrectly estimated, which can occur when device mismatches occur in the temperature sensor circuit.
What is desired is a single temperature-point temperature sensor circuit. A calibration method that measures the sensor circuit's output at only one temperature is desired. A method to adjust the sensor circuit's temperature sensitivity over a wide range or temperatures is desired. A calibration method that cancels DC offsets in the temperature sensor circuit is desired.